Impact tools

ABSTRACT

Impact tools are described which have an anvil system for transmitting force pulses generated by the hammer to a load. The anvil system includes an impact spring arrangement, the spring being either mechanical or liquid. In one embodiment the spring has a variable spring rate which changes under the duration of the force pulses. In the other embodiment the spring is operative to absorb the energy in the trailing end of the force pulse and return it to the hammer. In this manner, force pulses are transmitted which have a shape which may be efficiently utilized by the load.

United States Patent W s [4 1 May 16, 1972 1 IMPACT OOL 3,498,391 3/1970 Guild et al. ..173/131 72 Inventor: Boyd A. Wise, Webster, N.Y. 3932998 5/1962 [73] Assignee: General Dynamics Corporation Primary Examiner-David H. Brown An arti L K h 22 Filed: Jan. 29, 1970 M n [21] Appl. No.: 6,820 [57] I ABSTRACT lmpact tools are described which have an anvil system for 52 us. Cl ..173/131, 173/139 transmitting Pulses generated by the hammer a [51] Int. Cl ..B25d 9/04 The anvil system includes an impact spring arrangement the [58] Field of Search ..l73/l28 131 133 139- sPn'ng being either mechanical embdimm 6 the spring has a variable spring rate which changes under the duration of the force pulses. In the other embodiment the l 56] References and spring is operative to absorb the energy in the trailing end of the force pulse and return it to the hammer. In this manner, UNIT D S ES PATENTS force pulses are transmitted which have ashape which may be efficiently utilized by the load. 3,371,726 3/1968 Bouyoucos ..l85/56 X 3,446,293 5/1969 Guild et a]. ..l73/l31 18 Claims, 1 1 Drawing Figures PATENTEDMAY 16 I872 SHEET 2 [1F 3 INCREASED FORCE TJME- l-CUT OFF FORCE I408/48 140 FORCE ON STEEL FORCE ON STEEL WITH N0.| AND WITH NO. I SPRING ONLY No.2 SPRINGS T TIME 6 Pcs A TTORNE Y PATENTEDMAY 16 m2 3,662,843

SHEET 3 OF 3 MAx.FoRcE FORCE 90m A WISE TIME F69 I aw.

/ ATTORNEY IMPACT TOOLS The present invention relates to impact tools and particularly to an impact tool having an anvil system for the efiicient transfer of force pulses, generated upon the impact of a hammer, to a load.

The invention is especially suitable for use in percussive tools such as drills for earth boring purposes. Other applications for the invention will be found every where mechanical force pulses are generated and must be transferred to a load.

The present invention is an improvement upon the anvil system disclosed in my US. Pat. No. 3,382,932 issued May 14, 1968. That patent describes an anvil system utilizing an elastic member which has a stiffness or spring rate characteristic for shaping force pulses developed by an impact generator and delivering those force pulses to a load, especially the fonnation to be drilled. It is a feature of this invention to provide an anvil system, which not only affords a more precise shaping of the force pulses, but also utilizes the energy in the pulse which may not be absorbed by the load, so as to increase the efficiency of the generator which initially produces the pulses.

It is an object of the present invention to provide an improved anvil system for impact devices such as percussive tools.

It is a further object of the present invention to provide an improved impact spring arrangement for shaping force pulses for transmission to a load. 7

It is a further object of the present invention to provide an improved impact spring which becomes progressively stiffer as force is applied thereto so as to more accurately shape a force pulse prior to transmission thereof to a load.

It is a still further object of the present invention to provide an improved hydraulic impact spring.

It is a still further object of the present invention to provide an improved variable spring rate impact spring which shapes mechanical force pulses to provide greater energy in the portion of the pulse which is adapted to perform useful work.

It is another object of the present invention to provide improved impact devices such as percussive tools having higher efficiency. v

It is a still further object of the present invention to provide an improved anvil system for impact devices which translates impact force pulses into pulses for triangular shape having a controlled rise time and a precipitous decay time.

It is still another object of the present invention to provide an improved percussivev tool in which effective use is made of impact energy by returning a portion of such energy back to the force pulse generator so as to conserve energy that would otherwise be wasted and thus render the generator more efficient.

Briefly described, an impact tool embodying the invention includes a hammer element which is vibrated so as to impact upon an anvil system at least once during each cycle of vibration thereof. The anvil system in some versions includes an impact spring having a variable spring rate during the period of each of the pulses generated when the anvil system is impacted. The spring member may be a liquid or a mechanical spring. In order to increase the efficiencyof the system, the spring member may be effective to have increased stiffness as a function of the duration of the force pulse. Means may be included in the tool for limiting the deflection of the spring member to a predetermined deflection during the application of the force pulse. As the force pulse continues, its energy is stored in the spring and is returned to the hammer after the period of the force pulse delivered to the drill steel or load.

The invention itself both as to its organization and method of operation, as well as additional objects and advantages thereof, will become more readily apparent from a reading of the following description in connection with the accompanying drawings in which:

FIG. 1 is a diagrammatic, fragmentary, sectional view of a portionof an impact tool having an anvil system in accordance with an embodiment ofthe invention:

FIG. 2 is a view similar to FIG. 1 illustrating another embodiment of the invention;

FIG. 3 is still another view similar to FIG. 1 showing an impact tool in accordance with still another embodiment of the invention;

FIG. 4 is a pair of curves showing force pulses which are generated by an anvil system both with and without the impact springs in accordance with the embodiment of the invention shown in FIGS. 1-3;

FIG. 5 is a diagrammatic, fragmentary, sectional view of an impact tool and anvil system which is effective both for pulse shaping and for returning a portion of the pulse energy to the generator, the system being provided in accordance with an embodiment of the invention;

FIG. 6 shows curves of force pulses generated both with and without the impact spring arrangement shown in FIG. 5;

FIG. 7 is a schematic diagram of the equivalent circuit of the tool shown in FIG. 5;

FIG. 8 is a view similar to FIG. 5 of a portion of an impact tool in accordance with another embodiment of the invention;

FIG. 9 is a curve of force pulses generated by the device shown in FIG. 8;

FIG. 10 is a view similar to FIG. 5 of a portion of an impact tool in accordance with still another embodiment of the invention; and

FIG. 11 is another view similar to FIG. 5 of a portion of an impact tool in accordance with still another embodiment of the invention.

Referring more particularly to FIG. 1, there is shown an impact tool of the percussive type having a housing 10, including a force pulse generator 12, the hammer 14 of which is shown in FIG. 1. The hammer oscillates axially and repeatedly impacts an anvil system 16 including piston 18 and a shank 20. The shank may be mounted on a bearing 22 and may be connected to a drill steel (not shown) which in turn may be connected to a drill bit. The force pulse generator may be of the hydroacoustic type as described in my above referenced patent. The anvil system is configured to provide a variable spring rate liquid spring 24 which shapes the force pulses produced when the hammer impacts the piston.

The housing 10 has a first cavity 26 which may be liquid filled through porting means of the type described in my above referenced patent. The housing also has a second cavity 28 which communicates with a bore 30. A reduced diameter end 32 of the shank 20 is disposed in the bore 30. Seals for the purpose of confining the liquid, such as hydraulic oil, in the cavities 28 and 26 and preventing it from seeping through the open end of the bore 30 are not shown to simplify the illustration. Thus, bearing surfaces 34 are provided in the housing for guiding the piston 18. The end of the piston 18 which is adjacent to the shank 20 has a pair of reduced diameter portions 36 and 38. The portion 36 is adapted to enter the bore, suitable clearance being provided, so as to confine the liquid therein and form a first liquid spring 40. The bore has an enlargedportion 42 approximately the same diameter as the portion 38 of the piston. When the piston moves to the right, the shoulder 44 traps liquid in the opening 42 and defines a second liquid spring 46. The opening 42 is further enlarged to provide an opening 48 of approximately the same diameter as the diameter of the piston. Thus the shoulder 50, when it enters the opening 48, confines the liquid therein and defines a third liquid spring 52. Prior to impact, the shoulders 44 and 50 are clear of the openings so that when the first liquid Spring is effective, force is transferred via the liquid spring 40 to the shank 20 and thence to the load. As the piston moves further to the right, the other liquid springs are brought into play. By making the length of the second portion 38 longer than the first portion 36, the third liquid spring will be effective after the first the first and second liquid springs become effective.

define the liquid springs determine the stifiness-asa function of the movementof the 1 piston (viz. the, deflections of the spring). The spring stiffens The area of the shoulders which with deflection. .The spring rate, which is a function of the square of the areaof the shoulders and inversely of the length of the spring is desirably increased in the progression 1:4:16,

as each of the liquid springs 40, 46 and 52 are brought into play. Thus, if the spring cavity lengths are equal, the area of the shoulders 44 should be equal to the area of the end of the piston portion 36 and the area of the shoulder 50 three times the area of the end of the piston portion 36. Translated into diameters, the diameter of the shoulder 44 should be approximately 1.414 (the square root of two) times the diameter of the end of the portion 36 while the area of the shoulder 50 is l .414 times the diameter of the shoulder 44.

FIG. 2 shows an impact tool similar to that shown in FIG. 1 utilizing a variable spring rate mechanical spring in its anvil system 60. The force pulse generator includes a hammer 62 and the anvil system includes a shank 64 and a piston 66 guided in the housing 68 for movement as the hammer impacts the left end thereof. The piston 66 is made up of a rod 70 of elastic material such as steel. The end of the rod 70 has a stepped flange 72 which abuts the shank 64. Two cylinders of elastic material 74 and 76 are attached at the flange. The inner cylinder is shorter than the rod 70 so that the rod extends further towards the hammer. The outer cylinder 76 is still shorter than the inner cylinder 74.

In operation, the hammer first impacts the rod 70, drives it against the shank and causes it to deflect longitudinally. After some deflection, the hammer reaches the end of the inner cylinder 74 which thereupon deflects. The spring rate of the inner cylinder and the rods are then cumulative and the total spring rate of the piston increases. With further deflection between the rod and inner cylinders 70 and 74, the hammer reaches the end of the outer cylinder, which thereupon deflects and adds its spring rate and stiffness to the total effective spring rate and stiffness of the piston. Thus the stiffness of the spring rate of the piston is variable and increases in steps.

Referring to FIG. 3, the housing 80 of the tool includes a pulse generator, which may be of the type heretofore described, having a hammer 82. The anvil system 84 includes a shank 86 which is longitudinally movable in a bore 88 in the housing 80. The piston 90 is disposed within the bore 92 in the shank 86. The piston has three portions 94, 96 and 98 of different diameters. Prior to impact, clearances of progressively greater lengths D,, D and D are defined between the end 100 of the portion 92 and the shoulders 102 and 104 of the portions 96 and 98. The piston 90 is a mechanical spring made of elastic material such as steel. At the beginning of the force pulse, the end 100 is first brought into contact with the end 106 of the bore 92. Then the entire piston length is efiective in determining the stiffness and spring rate of the piston. When the portion 94 deflects so that the shoulder 102 abuts the end of the opening 108 in the shank 86, the effective length of the spring is the length of the portions 96 and 98. Further deflection of the piston brings the shoulder 104 into contact with the end 110 of the shank 86. Then only the length of the portion 98 is effective as the impact spring provided by the piston 90. Since the spring rate and the stiffness increase as the effective length of the piston spring 90 decreases, the stiffness increases stepwise with deflection of the impact spring provided by the piston 90.

FIG. 4 shows by the solid line curve the shape of the force pulse which is produced by means of the impact spring anvil arrangement shown in FIGS. 1-3. The dash line curves illustrate the effect of a constant spring rate impact spring. It will be noted that the maximum force of the spring is increased and that a larger portion of the energy is contained in the leading or early part of the pulse. As was explained in my above referenced patent, this shape force pulse is more effective since it is more effectively absorbed by the load as useful work and decreases reflections of energy back up the drill steel. Such reflections may cause the drill steel to fracture and, at a minimum, reduces the life of the drill steel by increasing fatigue thereof.

FIG. illustrates an impact tool wherein the anvil system provides a deflection switch which not only improves the force pulse shape but also increases the overall effectiveness of the drill by returning energy, which is not adapted to perform useful work at the load, back to the force pulse generator.

As in the tools illustrated in FIGS. 1-3 the tool is contained in a housing which also contains a force pulse generator which may be of the type described in my above referenced patent. The force pulse generator includes a hammer 122 which cyclically impacts an anvil system 124 including a piston 126 and a shank 128. The shank 128 is movable from left to right in a bore 130 in the housing 120 and may be connected via a drill steel to a drill bit. The piston 126 has a reduced diameter portion 132, the end 134 of which is disposed in the bore. Liquid is contained between the ends 136 of the shank 128 and the end 130 of the reduced diameter portion 132 of the piston 126. The ends 134 and 136 and the confined liquid therebetween define a first liquid spring 140.

The bore 130 is enlarged to define a cylindrical cup 142 which opens into a liquid filled cavity 144 in the housing 120. Normally a shoulder 146 of the piston 126 (before impact) is clear of the cup 142. It is only after a deflection D of the first liquid spring that the shoulder 146 enters the cup 142 and defines a second liquid spring 148. The second liquid spring is defined between the housing and the piston. Thus any deflection beyond D of the piston 126 the second spring 148 absorbs the force pulse and substantially little of it is transferred to the first liquid spring and thence to the shank 128. Since both spring 140 and 148 bear on the piston and thence the hammer, the motion of the hammer is reversed in a shorter time than would occur in the absence of the second spring 148. Once the motion of the hammer is reversed, energy is extracted from both springs, including energy that otherwise would have been imparted to the drill steel by spring 140.

The shape of the force pulse provided by the combination of the first and second liquid springs 140 and 148 is enclosed by the shaded area in FIG. 6. If the first liquid spring 140 were used, the force pulse would not taper off abruptly at its lagging end but would continue on as shown by the dash line. Immediately following the cut-off time I which takes place when the shoulder 146 enters the cup 142, the force that is transmitted to the shank drops sharply. The energy in the lagging portion of the pulse is returned to the piston and drives the piston to the left towards the hammer. This occurs when the hammer is moving away to the right. The left hand end 152 of the piston may contact the hammer or the liquid in the cavity 154 provides a medium for a transfer of the force stored in the second liquid spring back to the hammer. This additional energy is used in the operation of the force pulse generator and reduces the energy demanded thereby from its own power supply such as they hydraulic power supply described in my above referenced patent.

FIG. 7 illustrates the equivalent circuit of the tool shown in FIG. 5. The impact energy for the force pulse is developed as a velocity component (viz. current) through the inductance L presented by the mass of the hammer 122. This stored kinetic energy is effectively applied to the capacitance C of the first liquid spring and to the drill steel in parallel with it when the switch S opens, which takes place on hammer to piston contact. The switch S normally short-circuits the capacitance C presented by the second liquid spring 148, inasmuch as the shoulder 146 does not initially enter the cup 142. When the shoulder enters the cup S opens and the total capacitance seen by the hammer decreases. The amount of energy available in C is transmitted in part to the transmission line pcS represented by the shank 128 and the drill steel, and in part to the piston 126 and hammer 122, as the motion of the hammer is reversed. The foreshortening of the trailing edge of the pulse then results and the force is no longer transferred to the load, represented by the capacitance C,. Rather the energy is stored in C and is returned to the hammer, as the direction of the velocity V is reversed.

FIG. 8 illustrates another embodiment of the impact tool, this time utilizing only a single liquid spring.

A housing has a cavity 162 which may be liquid filled. A hammer 164 of a force pulse generator is mounted in the housing and impacts an anvil system 166 including a piston 168 and a shank 170. The shank is journaled for longitudinal motion in a bore 172 in the housing 160. A shoe 174 which has a bell shaped opening 176 is attached by screws 178 to the bottom 180 of the cavity 162. The shoe has a bore 182 in which the left end 184 of the shank is joumaled. The shank also has an enlarged base 186 which'is disposed in the cavity 176. The shoulder 188 of the base isseparated from the 'end 180 of the cavity 162 by a preset gap D. Liquid enters the cavity 176 in the shoe 174 via openings 190. The space in the bore 182 between the ends 1840f the shank 170 and the end 192 of the piston 168 is also liquid filled, and defines a liquid spring 194.

In operation, when the hammer impacts,force is transferred via the liquid spring 194 to the shank '170 until the shank moves the preset gap distance D. The liquid spring then can not transfer any more energy to the shank since the movement of the shank 170 is limited by the stop provided by the end 180 of the cavity 162. Energy is then stored in the liquid spring and is returned to the hammer 164 at the end of the force pulse. The shape of the force pulse has a rising leading edge and a sharply dropping lagging end as shown in FIG. 9.

FIG. shows an impact tool having a housing 200, a force pulse generator including a hammer 202 and an anvil system 204 made up of a piston 206 having a section 208 of elastic material such as spring steel which functions as a mechanical spring. The anvil system 204 also includes a shank 210 having a base 212, the rear shoulder 214 of which is disposed in a cavity 216. The rear end 218 of the cavity 216 is separated the shoulder 214 by a preset gap D. The mechanical spring then acts in a manner similar to the liquid spring 194 shown in FIG. 8. It will deflect until the shank moves the preset gap distance D. The energy is stored in the spring piston 206 and returned to the hammer at theend of the force pulse.

FIG. 11 shows an impact tool also having a force pulse generator of the type heretofore described with a hammer 220 which impacts an anvil system 222 including a piston 224 journalled for longitudinal motion in a bore 226 in a housing 228. The anvil system also includes a shank 230 which is also mounted in a bore 232 in the housing 228 and may move longitudinally. The shank 230 has an enlarged portion 234 disposed in a liquid filled cavity 236 in the housing 228. The enlarged portion has an axial blind hole 240 extending from the end 242 which is adjacent to the end 244 of a reduced diameter portion 246 of the piston 224. When the end 244 enters the hole 240, it defines a liquid spring 248 with the liquid contained in the hole 240. The rear end 250 of the enlarged portion 234 of the shank 230 separated from the rear wall 254 of the cavity 236 by a preset gap D.

The tool operates in a manner similar to that described in connection with FIG. 8 except that the liquid spring 248 is a part of the shank 230 itself.

From the foregoing description, it will be apparent that there has been provided an improved impact tool especially suitable for use in a percussive drill for earth boring applications. Other applications of the tool and variations and modifications of the herein described embodiments within the scope of the invention will undoubtedly suggest themselves to those skilled in the art. Accordingly, the foregoing descriptions should be taken as illustrative and not in any limiting sense.

What is claimed is:

1. A tool for impacting a load which comprises a. a hammer element b. an anvil system adapted to receive force pulses from said hammer element and to transfer said pulses to the load,

0. said anvil system including a spring member having a variable spring rate which is variable in steps over the duration of each of said force pulses.

2. The invention as set forth in claim 1 wherein said spring member has a plurality of portions each providing a different spring rate for said member.

3. The invention as set'forth in claim 2 wherein said member is a hydraulic spring 'having a plurality of active spring cavities of different areas.

4. The invention as set forth in claim 2 wherein member is a rod having a greater diameter.

said spring plurality of portions of successively 5. The invention as set forth in claim 2 wherein said spring member is a rod with at least one cylinder surrounding said rod, one of said rods and cylinder being slightly shorter than the other.

6. The invention as set forth in claim 1 wherein said anvil system includes a piston and a shank, said piston being disposed between said shank and said hammer, said piston comprising said spring member. 7

7, The invention as set forth in claim 6 wherein said tool includes a housing and wherein said spring member further comprises, said piston having a plurality of portions of progressively larger diameter at the end thereof adjacent said shank, said housing having acup shaped portion of progressively larger diameter, each slightly larger than said piston portions, into which said end portions of said piston enter when said piston is impacted by said hammer, said shank extending into said housing portion of smallest diameter, said housing being liquid filled in said cup shaped portions thereof to define a variable spring rate liquid spring.

8. The invention as set forth in claim 6 wherein said piston comprises a rod of elastic material a plurality of cylinders of elastic material encompassing and attached to said rod at the end thereof adjacent said shank, said cylinders each being progressively shorter than said r'od so as to be successively impacted by said hammer after said rod is impacted and deflects to the length of each of said shorter cylinders.

9. The invention as set forth in claim 6 wherein said piston is an elastic rod which extends into said shank said rod having portion of progressively larger diameter so as to define an end and a plurality of shoulders, said shank defining a plurality of stops each spaced from each other a distance slightly greater than said shoulders whereby the effective length of said rod is progressively shortened as said piston enters said shank so that the spring rate of said rod diminishes in steps with the motion of said piston into said shank.

10. A tool impacting a load which comprises a. a hammer element,

b. an anvil system adapted to receive force pulses from said hammer element and to transfer said pulses to the load,

c. said anvil system including a spring member in the transmission path of said force pulses to said load,

a housing in which said hammer and at least a portion of said anvil system are disposed, and

L means included in said housing for limiting the deflection of said spring member to a predetermined deflection during the application of said force pulse whereby a portion of said force pulse energy is stored in said spring member of said anvil system and is returned to said hammer after the period of said force pulse.

11. The invention as set forth in claim 10 wherein said anvil system includes a member movable in said housing toward and away from said hammer, said spring member includes a liquid spring defined by said housing and a portion of said anvil system member, after said anvil system has moved a predetermined distance in a direction away from said hammer.

12. The invention as set forth in claim 6 wherein said spring member includes an elastic member, and means on said elastic member for engaging said housing for limiting the movement thereof.

13. The invention as set forth in claim 10 wherein said spring member includes a body defining a liquid spring, means for mounting. said body in said housing so that said liquid spring is movable a predetermined distance upon impact of said anvil system by said hammer said distance being less than the travel of said hammer whereby a portion of the lagging end of said force pulse energy is absorbed in said spring and the transmission of said portion to said load is inhibited.

14. The invention as set forth in claim 10 wherein said anvil system includes a piston and a shank, said piston being disposed between said shank and said hammer, said piston having a reduced diameter portion at the end thereof adjacent said shank, said reduced diameter portion meeting the body of said piston at a shoulder, said housing having a longitudinal opening in which said shank and said reduced diameter portion are movably disposed with a body of liquid therebetween which define a first liquid spring, said housing having a cylindrical hole which enlarges the end of said opening on the side thereof adjacent said piston should and is substantially the same diameter as said piston body portion, said opening and said shoulder being disposed in liquid filled cavity in said housing so that said enlarged opening and shoulder define a second liquid spring of stiffness much greater than said first spring, said opening being of a length smaller than the length of said reduced diameter piston portion.

15. The invention as set forth in claim 10 wherein said anvil system includes a piston which provides said spring member, and a shank, said piston being disposed between said hammer and said shank, and means for limiting the travel of said shank under the force applied thereto by said piston after said shank executes a predetermined movement away from said hammer.

16. The invention as set forth in claim 15 wherein said housing defines a liquid filled chamber between opposed ends of said shank and said piston, said chamber being movable as said piston and shank move until said shank reaches said limiting means said piston and chamber providing a liquid spring.

17. The invention as set forth in claim 15 wherein said piston is an elastic rod which is compressed between said hammer and said shank.

18. The invention as set forth in claim 15 wherein said end of said shank opposed to said piston has an opening therein for receiving said piston with limited clearance, means providing a liquid filled chamber in said housing in which said opposed ends of said piston and shank and its openings are disposed, said opening and piston when inserted therein providing a liquid spring. 

1. A tool for impacting a load which comprises a. a hammer element b. an anvil system adapted to receive force pulses from said hammer element and to transfer said pulses to the load, c. said anvil system including a spring member having a variable spring rate which is variable in steps over the duration of each of said force pulses.
 2. The invention as set forth in claim 1 wherein said spring member has a plurality of portions each providing a different spring rate for said member.
 3. The invention as set forth in claim 2 wherein said member is a hydraulic spring having a plurality of active spring cavities of different areas.
 4. The invention as set forth in claim 2 wherein said spring member is a rod having a plurality of portions of successively greater diameter.
 5. The invention as set forth in claim 2 wherein said spring member is a rod with at least one cylinder surrounding said rod, one of said rods and cylinder being slightly shorter than the other.
 6. The invention as set forth in claim 1 wherein said anvil system includes a piston and a shank, said piston being disposed between said shank and said hammer, said piston comprising said spring member.
 7. The invention as set forth in claim 6 wherein said tool includes a housing and wherein said spring member further comprises, said piston having a plurality of portions of progressively larger diameter at the end thereof adjacent said shank, said housing having a cup shaped portion of progressively larger diameter, each slightly larger than said piston portions, into which said end portions of said piston enter when said piston is impacted by said hammer, said shank extending into said housing portion of smallest diameter, said housing being liquid filled in said cup shaped portions thereof to define a variable spring rate liquid spring.
 8. The invention as set forth in claim 6 wherein said piston comprises a rod of elastic material a plurality of cylinders of elastic material encompassing and attached to said rod at the end thereof adjacent said shank, said cylinders each being progressively shorter than said rod so as To be successively impacted by said hammer after said rod is impacted and deflects to the length of each of said shorter cylinders.
 9. The invention as set forth in claim 6 wherein said piston is an elastic rod which extends into said shank said rod having portion of progressively larger diameter so as to define an end and a plurality of shoulders, said shank defining a plurality of stops each spaced from each other a distance slightly greater than said shoulders whereby the effective length of said rod is progressively shortened as said piston enters said shank so that the spring rate of said rod diminishes in steps with the motion of said piston into said shank.
 10. A tool impacting a load which comprises a. a hammer element, b. an anvil system adapted to receive force pulses from said hammer element and to transfer said pulses to the load, c. said anvil system including a spring member in the transmission path of said force pulses to said load, d. a housing in which said hammer and at least a portion of said anvil system are disposed, and e. means included in said housing for limiting the deflection of said spring member to a predetermined deflection during the application of said force pulse whereby a portion of said force pulse energy is stored in said spring member of said anvil system and is returned to said hammer after the period of said force pulse.
 11. The invention as set forth in claim 10 wherein said anvil system includes a member movable in said housing toward and away from said hammer, said spring member includes a liquid spring defined by said housing and a portion of said anvil system member, after said anvil system has moved a predetermined distance in a direction away from said hammer.
 12. The invention as set forth in claim 6 wherein said spring member includes an elastic member, and means on said elastic member for engaging said housing for limiting the movement thereof.
 13. The invention as set forth in claim 10 wherein said spring member includes a body defining a liquid spring, means for mounting said body in said housing so that said liquid spring is movable a predetermined distance upon impact of said anvil system by said hammer said distance being less than the travel of said hammer whereby a portion of the lagging end of said force pulse energy is absorbed in said spring and the transmission of said portion to said load is inhibited.
 14. The invention as set forth in claim 10 wherein said anvil system includes a piston and a shank, said piston being disposed between said shank and said hammer, said piston having a reduced diameter portion at the end thereof adjacent said shank, said reduced diameter portion meeting the body of said piston at a shoulder, said housing having a longitudinal opening in which said shank and said reduced diameter portion are movably disposed with a body of liquid therebetween which define a first liquid spring, said housing having a cylindrical hole which enlarges the end of said opening on the side thereof adjacent said piston should and is substantially the same diameter as said piston body portion, said opening and said shoulder being disposed in liquid filled cavity in said housing so that said enlarged opening and shoulder define a second liquid spring of stiffness much greater than said first spring, said opening being of a length smaller than the length of said reduced diameter piston portion.
 15. The invention as set forth in claim 10 wherein said anvil system includes a piston which provides said spring member, and a shank, said piston being disposed between said hammer and said shank, and means for limiting the travel of said shank under the force applied thereto by said piston after said shank executes a predetermined movement away from said hammer.
 16. The invention as set forth in claim 15 wherein said housing defines a liquid filled chamber between opposed ends of said shank and said piston, said chamber being movable as said piston and shank Move until said shank reaches said limiting means said piston and chamber providing a liquid spring.
 17. The invention as set forth in claim 15 wherein said piston is an elastic rod which is compressed between said hammer and said shank.
 18. The invention as set forth in claim 15 wherein said end of said shank opposed to said piston has an opening therein for receiving said piston with limited clearance, means providing a liquid filled chamber in said housing in which said opposed ends of said piston and shank and its openings are disposed, said opening and piston when inserted therein providing a liquid spring. 